An empirical breakdown model of the gate oxide under current stress

Abstract

Intensive studies of gate oxide reliability have been made because of its impact on device performance and reliability. It is believed that oxide damage, such as interface states and broken bonds induced under high field and current injection stress, is in the form of generated traps (Apte and Saraswat, 1994; Schuegraf and Hu, 1994). However, the mechanisms of electron trapping are not clearly understood because of their sensitivity to the process and stress conditions (Huang et al, 1989; Dimaria et al., 1985; Lin et al., 1985; Eriguchi and Niwa, 1997; Rodriguez et al., 1998; Watt and Plummer 1987). TDDB using constant stress voltage or current is a well-known technique to characterize the gate oxide reliability. Under a constant voltage stress, it is difficult to determine the relationship between the amount of trapped charges and the stress current or electric field because the electric field and current varies with the amount of trapped charge during the stress. In this study, constant current stress was used to maintain a constant electric field during the stress and to monitor directly the amount of trapped charges with the gate voltage shift. The roles of the gate barrier height, SiO/sub 2/ gate oxide thickness, and temperature in the breakdown characteristics of gate oxides are discussed. Also, the maximum operating voltage and gate oxide lifetime are estimated using a new oxide breakdown model.